The Cube has the backup 5GHz connection.
The 60 GHz connection is reportedly more affected by rain (or fog):
http://forum.mikrotik.com/t/which-devices-for-a-wireless-link-between-two-buildings-100m-range/173870/1
On the other hand there have been reports of Cubes not being perfectly waterproof:
http://forum.mikrotik.com/t/getting-water-in-cubepro-and-cubeprosa/173409/2
From what I have read around (not any direct experience with any of them) I would go for the Cube, personally, but I would seriously think about finding some way to add some additional sealing on the outside or - if possible in the specific installation - to “protect” it from rain (and the idea - even if it will evidently void the warranty - to drill one or two drain holes doesn’t sound that bad to me).